Some apparatus are used to provide patients with air. This is used in many treatments. More frequently it is used for patients with a breathing deficiency caused for example by the weakness of the breathing system or by obstructive apneas during the sleep. In those cases it is important to control the pressure of the air delivered to the patient. With respiratory insufficient patients, apparatus providing air at a higher pressure help to compensate the weakness of the patients lungs. In the case of patients suffering of sleep apneas, providing the air at a higher pressure removes the obstruction of the upper airways.
Several kinds of apparatus are used. The CPAP (Continuous Positive Airway Pressure) apparatus provides a constant pressure to the patient. An enhancement of the CPAP is adjusting the pressure delivered according to the detection of events (snoring, apneas, hypopneas, . . . ) for example, those apparatus will increase pressure (within bounds) if events are detected and will reduce pressure (within bounds) if no events are detected during a defined duration. Other apparatus operate with two different levels of pressure, one for the inspiration phase, the other one for the expiration phase. They treat the sleep apnea disorder as well as some respiratory insufficient patients. Those apparatus are composed of a centrifugal blower which provides the air. This blower comprises an impeller which is rotated by an electrical motor using the brushless technology. The rotor is a multi poles permanent magnet and the stator is an electrical magnet with several crenels each of them having a winding. The windings are alternatively connected to a power source so that the magnetic field changes in the stator crenels enable the rotor to rotate.
These apparatus require efficient motors. In order to operate sensors are precisely positioned on the stator to detect the position of the rotor. The sensors are connected to a processor in order to provide the information concerning the position of the rotor. The processor is then able to drive the windings phases according to the rotor position. The efficiency of those motors is highly linked on the precision of the positioning of the sensors and the reliability of the system is linked to the reliability of the sensors. Those sensors detect the position of the rotor by the variations of the magnetic flow and thus their reliability depends also on their bandwidth. Standard sensors have usually a 10 kHz bandwidth and thus are not able to operate correctly at high speeds. Higher speeds can be provided by using sensors with a higher bandwidth but those sensors are expensive and still have a speed limitation. In fact the faster the rotor rotates the worse the detection is accurate, the less the motor is efficient. Sometimes the system can even stall. Because these problems of positioning and reliability, those air providing apparatus which are using these sensors do not use high speed motors. The provided pressure is proportional to the impeller rotation speed and to the size of the impeller. Thus, in order to have the required pressure the size of their impeller is increased. Mainly those apparatus use big impellers having a diameter comprised between 70 and 100 millimeters. Such impellers imply high inertia, thus preventing quick speed changes.
Moreover, in the case of a CPAP that does not require pressure changes within a breath, to have a well regulated pressure at the patient interface, these apparatus are requiring the use of a 22 millimeters diameter tube as the pressure drop within such a tube is negligible but the use of a smaller tube will not guarantee the pressure regulation A within acceptable bounds.
In the case of two levels of pressure apparatus, as changing the blower speed within a breath is impossible to achieve due to the high inertia, the highest level is delivered by the blower and the lowest is managed by using pneumatic valves, pressure dividers or alternative methods.
The size of the impeller, the sensor positioning and attachments and the number of wires required increase the size of the blower and thus of the apparatus. Furthermore the precise positioning of the sensors complicates the assembling of the motor implying an increase of the cost.
In US 2002/0000228, the inventors have used a way to obtain fast accelerations and decelerations which does not relies on the positioning of the rotor. US 2002/0000228 discloses a blower for an air assistance apparatus. The blower operates with an electric motor. The polarity of the stator's sectors are changed by a driving unit to achieve fast accelerations and decelerations in one patient's breath step. This result is obtained by using a compressor wheel with a very low mass and by holding the wheel without contact in the radial compressor. This system requires a lot of precision when assembling the motor to obtain the magnetic fields that will hold the wheel without contact in the compressor. The rotor position can not be determined.
Document U.S. Pat. No. 5,977,737 relates to a way to enhance the accuracy of the motor functions. The improvement of the accuracy is carried out by predicting the motor current. There are no means for sensing the motor current. The prediction of the motor current is made by using different parameters such as motor inductance, motor and driver resistance and the back-electo motor force (back-EMF) value. The motor's position may also be included as one of the parameters. Using these parameters the current is calculated. This allows the determination of the pulse widths to be applied to various inputs to the driver circuit. The back-EMF is not used to determine the rotor's position and to change the sector's polarity in respect of this position. U.S. Pat. No. 5,977,737 does not disclose a way to determine the rotor's position. The aspect disclosed by U.S. Pat. No. 5,977,737 is a more-accurate delivery of current and not a way for increasing the electro motor's efficiency. This document thus does not provide any indication to obtain fast accelerations and decelarations within a patient's breath.